Improved efficiency is required for a permanent magnet motor generator. Specifically, it is sometimes required that the power factor of a motor generator in a high-speed overload area be improved. With regard to a permanent magnet type motor generator, patent document 1 has disclosed the technology wherein when the magnetic flux axis of the permanent magnet is considered as a d-axis and an axis perpendicular to the d-axis is considered as a q-axis, the power factor can be increased by notching the q-axis side of the outer circumferential surface of the rotor core.
Furthermore, patent documents 2 and 3 have disclosed the configuration of a motor generator related to patent document 1.
Furthermore, reduction in the volume of a permanent magnet which accounts for a large portion of cost structure is required, and patent document 4 has disclosed the configuration of an embedded permanent magnet type motor generator. According to patent document 4, magnetic flux of the permanent magnet is increased to reduce the d-axis side reactance and simultaneously the q-axis side reactance is reduced Therefore, as the result of reduction of magnetic flux that generates reluctance torque, reactance in the high-speed load area is reduced thereby improving the power factor.    [Patent document 1] Japanese Patent Laid-Open No. 2006-101608    [Patent document 2] Japanese Patent Laid-Open No. 2002-78255    [Patent document 3] Japanese Patent Laid-Open No. 2001-145284    [Patent document 4] Japanese Patent Laid-Open No. Hei 10 (1998)-126985